Greenwave EMI Meter Review

[solderdude]

A real EMI receiver, which requires specialized probes/antennae and calibration can be found here.
They are just slightly more expensive and can show EMI a bit more detailed.

High levels of RF radiation can indeed be bad for audio gear - it can cause noise in the audio no matter how good the audio gear's power supply filtering is. But there has to be really VERY high levels of RF for this to happen.

Yep... the tested meter might just be somewhat indicative for mains noise.
Most mains noise is common mode, meaning it is not present between L and N but present in both lines in (about equal) amplitude opposite the ground we walk on.

Even outside that, the metal boxes of audio gear provides strong immunity against RF incursion unless it is insanely strong.

Not exactly... I have done quite a lot of such testing (at an EMC lab) and can say with absolute certainty that even a small piece of not screened wire connected to a device can mean RF can enter nearly unattenuated. Speaker wires, mains cords, even shielded cables when the shield is not directly connected to the enclosure.
That said... for this to become audible it needs to be high enough for 'AM detection' in audio gear.

they get demodulated into AM, then sure, if you are hearing such noise, you want to investigate the source. I have only heard of this with long wires and closeness to powerful radio stations.

Indeed.

So RF noise can't generate audible-band distortion.

Yes it can. IM for instance or beating against internal clocks. It would have to be unusually high though. Also common mode and leakage currents can enter audio paths.

When one is concerned about RF incursion do the following simple test.
Open a device you want to check.
Put your cellphone in it.
Close the device again.
Call your phone.
When it rings there is RF leaking inside the device.
Of course this only proves 1GHZ or 2GHz band is able to enter and may yet be O.K. for radio etc.

 

[pma]

Not exactly... I have done quite a lot of such testing (at an EMC lab) and can say with absolute certainty that even a small piece of not screened wire connected to a device can mean RF can enter nearly unattenuated. Speaker wires, mains cords, even shielded cables when the shield is not directly connected to the enclosure.

I agree with you. I was designing measuring amplifiers and optoelectronic systems for high voltage and high current testing laboratories and confirm that audio devices are in fact very poorly designed and constructed re high frequency EMI immunity. I also have plenty of measurements in my database measured with GHz spectrum analyzers. I confirm that even 1 cm of unshielded wire going inside the shielding box without proper HF feedthrough brings the EMI inside the component. Also audio connectors and their insulated placement on the metal case are inefficient to prevent HF fields from penetrating into the instrument.

 

[MacCali]

Came across the KVAR box, not sure if you guys have heard of it. When looking into that I found this “more” advanced one and funny they’re using this greenwave meter.

*this has nothing to do with home audio

 

[wwenze]

Good guy greenwave meter, helping to identify bogus videos and saving precious time.

 

[Softimage]

This review and final assessment is not based on real experiences with dirty electric. The Greenwave meter doesn't need to be accurate down to or below 1 kHz. The whole point of the meter is to measure "relative" reductions from EMI filtering. Refrigerators, microwaves, light bulbs, wiring shorts, hairdryers, space heaters, and computers ARE going to produce a certain level of noise into your speakers. Just turning on a computer that shares the same circuit as your studio monitors will instantly produce 900 mV to 1,200 mV of EMI. This is not debatable; it's an observable fact that you can experiment with yourself. Professional studios create expensive isolated circuits all the way back to the electrical panel so they can keep EMI from other devices OUT of their audio network. Do you really think you are getting clean electricity from your public power grid into your house or apartment? Think again! You are already getting a measurable 500 mV to 1,000 mV of dirty electric just from your public power grid.

 

[fpitas]

This review and final assessment is not based on real experiences with dirty electric. The Greenwave meter doesn't need to be accurate down to or below 1 kHz. The whole point of the meter is to measure "relative" reductions from EMI filtering. Refrigerators, microwaves, light bulbs, wiring shorts, hairdryers, space heaters, and computers ARE going to produce a certain level of noise into your speakers. Just turning on a computer that shares the same circuit as your studio monitors will instantly produce 900 mV to 1,200 mV of EMI. This is not debatable; it's an observable fact that you can experiment with yourself. Professional studios create expensive dedicated circuits all the way back to the electrical panel so they can keep EMI from other devices OUT of their audio network. Do you really think you are getting clean electricity from your public power grid into your house or apartment? Think again! You are already getting a measurable 500 mV to 1,000 mV of dirty electric just from your public power grid.

Uhm...and most competent equipment filters it quite effectively. Do you sell these things, or something?

 

[MacCali]

This review and final assessment is not based on real experiences with dirty electric. The Greenwave meter doesn't need to be accurate down to or below 1 kHz. The whole point of the meter is to measure "relative" reductions from EMI filtering. Refrigerators, microwaves, light bulbs, wiring shorts, hairdryers, space heaters, and computers ARE going to produce a certain level of noise into your speakers. Just turning on a computer that shares the same circuit as your studio monitors will instantly produce 900 mV to 1,200 mV of EMI. This is not debatable; it's an observable fact that you can experiment with yourself. Professional studios create expensive dedicated circuits all the way back to the electrical panel so they can keep EMI from other devices OUT of their audio network. Do you really think you are getting clean electricity from your public power grid into your house or apartment? Think again! You are already getting a measurable 500 mV to 1,000 mV of dirty electric just from your public power grid.

B&K has a machine that can produce such dirty power that no company can produce to the public.

When you measure a unit with the dirty dirty there is no audible difference to the output of the unit.

Amir has shown us this. Also if you do fancy clean power this unit is cheaper and provides far superior clean power to any of your equipment. Just grab one so you can sleep better at night.

*It can provide clean and dirty, your choice by selection

 

[Softimage]

Uhm...and most competent equipment filters it quite effectively. Do you sell these things, or something?

Well, if that's your personal opinion... then I guess you can make a personal visit to all of the sound studios, churches, and hospitals with isolated electric circuits and tell them they know nothing about EMI and ground loops.

 

[fpitas]

Well, if that's your personal opinion... then I guess you can make a personal visit to all of the sound studios, churches, and hospitals with isolated electric circuits and tell them they know nothing about EMI and ground loops.

It's odd that Amir can't reproduce the results you claim. I'm sure that studios go to great lengths, on the off chance that a session may get ruined. That's expensive. But for home use? I think you're barking up a non-existent tree.

 

[NTK]

Here is the link to Amir's study.

Impact of AC Distortion & Noise on Audio Equipment

This is an ASR research project to see what impact AC noise and distortion has on performance of audio equipment. I have been wanting to write this article some three years ago and finally getting a chance to do the testing and release it. As you will see, the heart of this study is a special...

www.audiosciencereview.com

TL/DR summary:
Test conditions:

1. Regenerated AC, 0.06% THD​

2. AC from Amir's house sockets, 1.9%THD​

3. Simulated light dimmer (phase angle chopped AC), 18% THD​

Results:

Made no difference to the performance of the devices tested, except for California Audio Labs Sigma DAC which went a bit unstable (noise floor fluctuation) with the simulated light dimmer AC.​

 

[robwpdx]

This is a review and detailed measurements of the Greenwave Broadband EMI Meter. It was kindly drop shipped to me by a member and costs US $135.
View attachment 279763
The device is simple: you plug in the AC cord (see on the bottom) into an AC outlet which both powers the unit and shows/sounds a couple of values and buzzes through the small speaker. They are quite popular at audio shows to demonstrate the before and after effect of power filters. The unit attempts to show both before and after levels in blue LED above but it is subject to failure as you see above. It seems to sample the noise level and if there is a change, it shows a new value. This works sometimes if you plug it in just right. Otherwise, the mere act of plugging in the unit causes it to read differing measurements, making it think a filter has been added to the circuit.

Company provides scant specification for the unit:
View attachment 279765
But what is there should be an alarm to audio users as the lowest measured frequency is 3 kHz. And the highest 10 MHz. In other words, bulk of what it measures is above audible band.

I was originally hope to try to find its frequency response and linearity but sweeping an input tone through it. Alas, since it combines AC power with source of noise measurement, this was not easily feasible (I would have to build a high-voltage noise injection interface). So I resorted to just some spot checks as you see below.

Greenwave EMI Meter Measurements
As always, I start my measurements with the noise and spectrum of my "raw" AC mains power strip which has a number of devices plugged into it:
View attachment 279766
We see that the bulk of the harmonic noise and distortion is under 1 kHz. Therefore measuring from 3 kHz as the Greenwave meter performs, is of little value. Still, I plugged the unit in, only to have it overflow (it shows 1---).

So I went the other extreme and tested it with my B&K 9801 Lab AC generator. This is its spectrum:
View attachment 279767

We see far cleaner output with second harmonic at -74 dB. Total noise+distortion has dropped from 2.5% to 0.05%. Here is what the meter shows now:

View attachment 279768

On one hand it is correctly showing lower value. On the other hand, the buzzing noise it made was much louder than when fed from my "dirty" Raw mains! I don't know what it is using to source that noise. I briefly "powered" the unit with my analyzer and the pitch increased with the input frequency. So it seems to be just be feeding AC into that speaker but then I don't know how it would make noise in response to ultrasonics. I would think that it would need to demodulate the input waveform. Regardless of what it does, I would ignore the noise. Alas, it is quite annoying so I wished it had an on off switch for that.

That's all I have for you.

Conclusions
Directionally, the testing shows that the meter in there is showing something proportion to level of input noise. How correct it is, is hard to say. The fact that company documents it to work from 3 kHz and up, should automatically disqualify it from usage for audio. I know some audiophiles think any radiation is bad but remember, your equipment internally performs massive filtering of such high frequencies. Yes, there are rare cases of AM radio leaking into circuit but unless that is what you are facing, do not confuse noise over AC line with noise level inside the power circuits of your audio gear!

I can't recommend the Greenwave Broadband EMI meter. I think it easily misleads people to spend money on power tweaks which have no value as far as improving your audio gear.

------------
As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Thanks for the review.

In the electric utility world the term is power quality. That would cover harmonics beyond the fundamental 50/60 Hz and noise.

Electricity customers who have money, like data centers, research laboratories, and hospitals can buy or rent (expensive) power quality test equipment. Vendors of "power quality analyzers" include https://www.dranetz.com/. Usually they have a recording capability to capture time-varying problems and one-time noise events.

Usually the big generators connected through large transformers with very limited high frequency pass through are relatively clean. That would include inverter-based generators like wind and solar. The big generators are connected to the wholesale grid which drops off in each city to typically an ~100KV grid connecting all the neighborhood substations. The low voltage side of the substation transformer about 10-30KV branches out to the homes and businesses in a tree structure of feeders. 1 or more phases pass houses. There are pole transformers or ground mounted transformers to each meter.

Every time someone turns on or off a light switch, uses a light dimmer, runs an LED bulb, the refrigerator or HVAC turns on or off, or any switching power supply wall wart injects noise on the line. In the big power system, the feeders are where the line disturbances are. They are all shared by neighbors sharing a pole transformer.

This article discusses power transformer frequency response: https://www.dv-power.com/fundamental-understanding-of-frequency-response-characteristic/

Our audio equipment power supply and all the bypass capacitors on the power to gain stages usually filters them out.

If someone wanted to spend money, and recording studios do, you could build a separate earth ground to be the signal ground for all your equipment, study how the chassis/safety ground is implemented and possibly modify it, then insure no ground loops. Or one could run all their audio equipment line power through its own in-home isolation transformer like a https://www.power-solutions.com/ups...n-power-conditioners/eaton-power-suppress-t7/. Or one could run all their equipment on batteries which is becoming cheaper every day.

 

[fpitas]

Just the other day I was wondering what the FR of a utility transformer is.

 

[robwpdx]

A real EMI receiver, which requires specialized probes/antennae and calibration can be found here.
They are just slightly more expensive and can show EMI a bit more detailed.


Yep... the tested meter might just be somewhat indicative for mains noise.
Most mains noise is common mode, meaning it is not present between L and N but present in both lines in (about equal) amplitude opposite the ground we walk on.


Not exactly... I have done quite a lot of such testing (at an EMC lab) and can say with absolute certainty that even a small piece of not screened wire connected to a device can mean RF can enter nearly unattenuated. Speaker wires, mains cords, even shielded cables when the shield is not directly connected to the enclosure.
That said... for this to become audible it needs to be high enough for 'AM detection' in audio gear.

Indeed.


Yes it can. IM for instance or beating against internal clocks. It would have to be unusually high though. Also common mode and leakage currents can enter audio paths.

When one is concerned about RF incursion do the following simple test.
Open a device you want to check.
Put your cellphone in it.
Close the device again.
Call your phone.
When it rings there is RF leaking inside the device.
Of course this only proves 1GHZ or 2GHz band is able to enter and may yet be O.K. for radio etc.

Thanks. We should probably have a separate thread for radio interference. I have also worked in radio on mobile wireless standards and futures. One of my professors studied RF and the body and I have looked at the literature on that. ASR has a deep bench of experts.

 

[milosz]

You say >>Refrigerators, microwaves, light bulbs, wiring shorts, hairdryers, space heaters, and computers ARE going to produce a certain level of noise into your speakers.<<

Please provide reference to peer-reviewed papers which show this, or provide your own data and methods. FYI, just saying something does not make it so.

 

[fpitas]

You say >>Refrigerators, microwaves, light bulbs, wiring shorts, hairdryers, space heaters, and computers ARE going to produce a certain level of noise into your speakers.<<

Please provide reference to peer-reviewed papers which show this, or provide your own data and methods. FYI, just saying something does not make it so.

With all that electrical bedlam going on, it's odd that none of us have noticed it, either.

 

[milosz]

All the things going on and off on the power line - not just in your home, but in any other loads that are on the same distribution transformer; the noise put into the line by switchmode power supplies like computers, cell charges and what not; noisy electrical motors, lamp dimmers using noisy SCR circuits => all these things put noise on the POWER LINE. This noise does not get to your speakers unless you are using really low quality gear, or you have your speakers connected directly across the power line - in which case you will have other problems....

 

[CleanSound]

I have one. It's a measurement tool and gives you accurate data, it is up to the user to decide what to do with that data, if any action at all. Just like a SPL meter, an oscilloscope or multimeter.

It wasn't expensive. I use it to understand my power, it can also help me know the crap that a SMSP is spitting back out to my AC line, I have some very sensitive equipment in the house, so it helps me determine how to isolate those sensitive equipment from the noise regurgitation from endless of SMPS around the house.

 

[fpitas]

I was curious if these devices were sold as audiophile tweaks so I looked the company up.

It's worse than that - they're sold as HEALTH devices. This company is trying to convince you that noise in your power lines is bad for your health.

Absolute scumbags.

There's a whole cult of believing that EMI from, for example, nearby cell towers, high tension lines etc. is killing us all.

 

[SuicideSquid]

There's a whole cult of believing that EMI from, for example, nearby cell towers, high tension lines etc. is killing us all.

I worked for our provincial government when smart electricity metres were introduced. I had to deal with a lot of these whackjobs.